A multi-tier architecture (also referred to as a “multi-layered architecture) is used to implement a set of servers (also referred to as a “server stack”) and/or other devices for executing various applications. Each tier is assigned a different role. One common structure is the three-tiered architecture, including the following ordered list of tiers: (a) presentation, (b) application, and (c) storage. As an example, a presentation tier may include a web browser that renders static and/or dynamic content; an application tier may include an engine using some dynamic Web content technology (such as ASP, CGI, ColdFusion, Dart, JSP/Java, Node.js, PHP, Python or Ruby on Rails); a storage tier may include a database. The web browser may generate a user interface, which is used to accept user input and present information to a user. Based on user input, the web browser may send requests to the application tier. The application tier may service the requests, which may include making queries and/or updates against the database.
Servers associated with the presentation tier may be referred to as “presentation servers.” Servers associated with the application tier may be referred to as “application servers.” Servers associated with the storage tier may be referred to as “storage servers.”
Any number of tiers may be used in a multi-tier architecture. In some cases, the application layer may be further sub-divided into more fine-grained tiers. In some cases, an integration tier may be added as an additional tier. The integration tier may provide an interface (such as, an application programming interface (API)) for accessing data in the storage tier. The integration tier may be implemented between the application tier and the storage tier.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.